The conventional wireless communication system includes a mobile station (MS) and a base station (BS) providing a service in a specific region called a cell. Changes in a wireless environment may have an effect on quality of a signal transmitted in a radio channel between the MS and the BS. In particular, due to various factors in a surrounding environment, such as scatters, movement of the MS, etc., a wireless channel changes over time. In addition, there is a restriction in terms of a distance since reception power is rapidly decreased in proportion to a distance between wireless communication entities. Therefore, in general, the MS can communicate with the BS when the MS is located within the coverage of the BS. As such, due to several factors such as the scatters, a movement speed of the MS, a distance between transmission and reception, etc., a maximum transfer rate, a throughput of an intra-cell user, and a throughput of a whole cell are decreased between the BS and the MS. For example, when the MS is located in a cell boundary or when an obstacle such as a building exists between the MS and the BS, communication quality between the MS and the BS may not be satisfactory.
As an effort to overcome the aforementioned problem, the wireless communication system may employ a relay. The relay is a device for relaying a signal between the MS and the BS. By allowing the relay to employ various techniques capable of compensating for deterioration of a signal transmitted between the BS and the MS, it is expected to achieve an effect of coverage extension or the like.
The relay can be classified into L1, L2, and L3 relays according to a supported function or protocol layer. In brief, the L1 relay is a relay that retransmits a received signal by simply amplifying the signal, the L2 relay is a relay capable of performing a function for decoding the received signal and then encoding the signal, the L3 relay is a relay capable of transmitting a physical cell ID (PCI), a synchronization signal, a reference signal, and a control channel which are different from those of the BS.
If the relay is the L3 relay, the MS regards the relay as an independent BS, and backward compatibility with the legacy MS can be easily achieved. On the other hand, if the relay is the L2 relay, for an effective operation of the relay, the BS needs to perform management on whether to establish a connection between the relay and the MS to be connected to the relay.